Predation

1. Predation

2. Hypotheses for Patterns of Diversity • Evolutionary Time • Ecological Time • Primary Production • Stability of Primary Production • Structural (Habitat) Diversity • Climatic Stability • Competition • Predation

3. Predation • In an ecological sense, predation is not just carnivores like wolves eating musk oxen, or coyotes eating mice. • In fact, deer are acting as predators on plants, parasites act as predators on their hosts, and mice act as predators on the seeds they eat. • The difference here is in the extent of the effect.

4. Predation • Carnivory – capture, kill, and consume an animal. • Herbivory – consumption of plant material by an animal. • Grazer/folivore consumes leafy material • Browser consumes woody material and bark. • Granivore consumes seeds • Frugivore consumes fruit • Exudivore consumes exudates like sap.

5. Predation • Parasitism – association w/ host. Objective is to keep host alive. Generally, parasite stays with same host throughout its life. • Parasitoids – parasitic activities limited to larval stages.

6. Predation • Carnivorous predation: • predator must locate, capture, and consume prey. • Mammalian predators employ a diversity of morphological, physiological, and behavioral techniques to to this. • Reptilian predators do this as well. Compare a monitor lizard with a snake.

7. Predation • Prey detection and recognition • Search image. • Smell - chemoreception • Sound - bats and marine carnivores. • Prey capture • Stalk and ambush • Finess. • Pure power.

12. Prey Adaptations • Avoiding detection • Crypsis • Avoiding capture • Herd behavior in ungulates = safety in numbers and increased vigilance. • Detection of predator as in kangaroo rats. • High speed locomotion, or use of refugium. • Display as in baboons. • Chemical defense as in skunks and toads. • Body armor as in turtles.

17. Herbivorous Predation • Herbivores use a variety of devices to improve efficiency: • Pectinate teeth in dermopterans. • Thumb in giant panda • Elongated intestines and ceacum and/or ruminant stomach.

19. Plant Adaptations to Herbivores • Chemical defenses such as tanins • Grey and fox squirrels and red and black oak acorns. • Synchronous flowering or seed set ‘swamps’ potential herbivores – safety in numbers. • Structural adaptations – spines in cacti and euphorbs.

20. Effects of Herbivory • For the most part, herbivory is not good for the plant. However, • Grazing may increase production in some cases.

21. Optimal Foraging • Predators are under intense selection pressure to find and consume prey. • We expect that organisms should forage in a way that optimizes their inclusive fitness. • How can this be done? • 2 ways: Energy Maximizers and Time Minimizers.

22. Energy maximizers: Get maximum possible energy return under a given set of foraging conditions – EMs get the maximum amount of energy possible. Time minimizers: Get maximum possible energy return under a given set of foraging conditions – TMs obtain a given amount of energy in the min. amt. of time. Optimal Foraging

23. Optimal Diet • There is a trade-off between a specialized diet and a generalized one: • Specialized diet: food items are of high value, but may require extensive search energy or search time. These items may also require extensive handling. • Generalized diet: food items may be more abundant, but will not be of equal value.

24. Optimal Foraging • Each item consumed contributes to the average energy input. The better diet is the one that increases the average energy input. • The question becomes, should the organism broaden its diet or narrow its diet?

25. Optimal Foraging • Energy input per item can be written as:

26. Optimal Foraging • In this formulation, we compare the caloric content of each item, to the handling time (or energy) required to capture, subdue, and consume that item. • Lets create a model that will allow us to predict what an organism should do.

27. Optimal Foraging • Define the amount of time spent searching for prey as Ts seconds. • Our predator encounters 2 types of prey at rates 1 and 2 prey per second. • These prey items contain E1 and E2 calories, and take h1 and h2 seconds to handle.

28. Optimal Foraging • If the predator spends Ts seconds searching for prey, it will encounter: n1 = Ts1 type 1 prey n2 = Ts 2 type 2 prey

29. Optimal Foraging • The total energetic return, E, will be equal to the number of encounters times their respective energetic contents. E = n1E1 + n2E2

30. Optimal Foraging • The total time spent handling these prey items will be: Th = n1h1 + n2h2

31. Optimal Foraging • Substituting for n1 and n2, we get:

32. Optimal Foraging • The total time spent handling prey is given by:

33. Optimal Foraging • So, the total time spent searching for and handling prey will be:

34. Optimal Foraging • And the energetic return per unit time spent searching for and handling prey becomes:

35. Optimal Foraging • This simplifies to:

36. Optimal Foraging • Try an example. Suppose our optimal forager has 100 seconds to search for prey. It encounters prey type 1 at a rate of 0.10/s, and prey type 2 at 0.01/s. Thus, • 1 = 0.1 • 2 = 0.01

37. Optimal Foraging • Also, prey type 1 contains 10 calories and takes 5 seconds to handle, while prey type 2 contains 10 calories and takes 10 seconds to handle. • E1 = 10 E2 = 10 • h1 = 5 h2 = 10 • Should our predator be a generalist or a specialist?

38. Marginal Value Theorem

39. Marginal Value Theorem